diff --git a/src/main/java/com/google/devtools/build/lib/actions/Artifact.java b/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
index 1ed8df5..d6c610e 100644
--- a/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
+++ b/src/main/java/com/google/devtools/build/lib/actions/Artifact.java
@@ -29,6 +29,7 @@
 import com.google.devtools.build.lib.actions.ActionAnalysisMetadata.MiddlemanType;
 import com.google.devtools.build.lib.actions.ArtifactResolver.ArtifactResolverSupplier;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.concurrent.BlazeInterners;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
 import com.google.devtools.build.lib.shell.ShellUtils;
@@ -662,9 +663,9 @@
    */
   public final PathFragment getRunfilesPath() {
     PathFragment relativePath = rootRelativePath;
-    if (relativePath.startsWith(Label.EXTERNAL_PATH_PREFIX)) {
+    if (relativePath.startsWith(LabelConstants.EXTERNAL_PATH_PREFIX)) {
       // Turn external/repo/foo into ../repo/foo.
-      relativePath = relativePath.relativeTo(Label.EXTERNAL_PATH_PREFIX);
+      relativePath = relativePath.relativeTo(LabelConstants.EXTERNAL_PATH_PREFIX);
       relativePath = PathFragment.create("..").getRelative(relativePath);
     }
     return relativePath;
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/Runfiles.java b/src/main/java/com/google/devtools/build/lib/analysis/Runfiles.java
index 1d8e23f..477764e 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/Runfiles.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/Runfiles.java
@@ -24,7 +24,7 @@
 import com.google.devtools.build.lib.actions.Artifact;
 import com.google.devtools.build.lib.actions.ArtifactPathResolver;
 import com.google.devtools.build.lib.analysis.configuredtargets.RuleConfiguredTarget.Mode;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
 import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
 import com.google.devtools.build.lib.collect.nestedset.Order;
@@ -554,7 +554,7 @@
     }
 
     private PathFragment getExternalPath(PathFragment path) {
-      return checkForWorkspace(path.relativeTo(Label.EXTERNAL_PACKAGE_NAME));
+      return checkForWorkspace(path.relativeTo(LabelConstants.EXTERNAL_PACKAGE_NAME));
     }
 
     private PathFragment checkForWorkspace(PathFragment path) {
@@ -564,7 +564,7 @@
     }
 
     private static boolean isUnderWorkspace(PathFragment path) {
-      return !path.startsWith(Label.EXTERNAL_PACKAGE_NAME);
+      return !path.startsWith(LabelConstants.EXTERNAL_PACKAGE_NAME);
     }
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/commands/SyncCommand.java b/src/main/java/com/google/devtools/build/lib/bazel/commands/SyncCommand.java
index 81299e3..843f9bd 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/commands/SyncCommand.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/commands/SyncCommand.java
@@ -19,7 +19,7 @@
 import com.google.devtools.build.lib.analysis.NoBuildEvent;
 import com.google.devtools.build.lib.analysis.NoBuildRequestFinishedEvent;
 import com.google.devtools.build.lib.bazel.repository.RepositoryOrderEvent;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
 import com.google.devtools.build.lib.events.Event;
@@ -98,7 +98,7 @@
                   env.getCommandId().toString())));
 
       // Obtain the key for the top-level WORKSPACE file
-      SkyKey packageLookupKey = PackageLookupValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+      SkyKey packageLookupKey = PackageLookupValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
       LoadingPhaseThreadsOption threadsOption = options.getOptions(LoadingPhaseThreadsOption.class);
       EvaluationContext evaluationContext =
           EvaluationContext.newBuilder()
@@ -117,7 +117,7 @@
       }
       RootedPath workspacePath =
           ((PackageLookupValue) packageLookupValue.get(packageLookupKey))
-              .getRootedPath(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+              .getRootedPath(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
       SkyKey workspace = WorkspaceFileValue.key(workspacePath);
 
       // read and evaluate the WORKSPACE file to its end
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
index 375cfea..62f5e14 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/skylark/SkylarkRepositoryFunction.java
@@ -20,7 +20,7 @@
 import com.google.devtools.build.lib.analysis.RuleDefinition;
 import com.google.devtools.build.lib.bazel.repository.RepositoryResolvedEvent;
 import com.google.devtools.build.lib.bazel.repository.downloader.HttpDownloader;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.packages.Rule;
 import com.google.devtools.build.lib.rules.repository.RepositoryDelegatorFunction;
@@ -169,7 +169,7 @@
           new IOException(rule + " must create a directory"), Transience.TRANSIENT);
     }
 
-    if (!outputDirectory.getRelative(Label.WORKSPACE_FILE_NAME).exists()) {
+    if (!outputDirectory.getRelative(LabelConstants.WORKSPACE_FILE_NAME).exists()) {
       createWorkspaceFile(outputDirectory, rule.getTargetKind(), rule.getName());
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java
index 5583042..afb58ea 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java
@@ -58,7 +58,7 @@
 import com.google.devtools.build.lib.bazel.rules.workspace.MavenServerRule;
 import com.google.devtools.build.lib.bazel.rules.workspace.NewGitRepositoryRule;
 import com.google.devtools.build.lib.bazel.rules.workspace.NewHttpArchiveRule;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.packages.Attribute.LabelLateBoundDefault;
 import com.google.devtools.build.lib.rules.android.AarImportBaseRule;
 import com.google.devtools.build.lib.rules.android.AndroidConfiguration;
@@ -209,7 +209,7 @@
         public void init(ConfiguredRuleClassProvider.Builder builder) {
           builder
               .setPrelude("//tools/build_rules:prelude_bazel")
-              .setRunfilesPrefix(Label.DEFAULT_REPOSITORY_DIRECTORY)
+              .setRunfilesPrefix(LabelConstants.DEFAULT_REPOSITORY_DIRECTORY)
               .setPrerequisiteValidator(new BazelPrerequisiteValidator())
               .setActionEnvironmentProvider(SHELL_ACTION_ENV);
 
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonSemantics.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonSemantics.java
index 0ff5d15..31b6275 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/python/BazelPythonSemantics.java
@@ -39,7 +39,7 @@
 import com.google.devtools.build.lib.analysis.actions.TemplateExpansionAction;
 import com.google.devtools.build.lib.analysis.configuredtargets.RuleConfiguredTarget.Mode;
 import com.google.devtools.build.lib.analysis.test.InstrumentedFilesCollector.InstrumentationSpec;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
 import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
 import com.google.devtools.build.lib.rules.cpp.CcInfo;
@@ -236,7 +236,7 @@
   }
 
   private static boolean isUnderWorkspace(PathFragment path) {
-    return !path.startsWith(Label.EXTERNAL_PATH_PREFIX);
+    return !path.startsWith(LabelConstants.EXTERNAL_PATH_PREFIX);
   }
 
   private static String getZipRunfilesPath(PathFragment path, PathFragment workspaceName) {
@@ -246,7 +246,7 @@
       zipRunfilesPath = workspaceName.getRelative(path).toString();
     } else {
       // If the file is in external package, strip "external"
-      zipRunfilesPath = path.relativeTo(Label.EXTERNAL_PATH_PREFIX).toString();
+      zipRunfilesPath = path.relativeTo(LabelConstants.EXTERNAL_PATH_PREFIX).toString();
     }
     // We put the whole runfiles tree under the ZIP_RUNFILES_DIRECTORY_NAME directory, by doing this
     // , we avoid the conflict between default workspace name "__main__" and __main__.py file.
diff --git a/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java b/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
index 4ed8fda..d4ce23d 100644
--- a/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
+++ b/src/main/java/com/google/devtools/build/lib/buildtool/SymlinkForest.java
@@ -20,7 +20,7 @@
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.concurrent.ThreadSafety;
 import com.google.devtools.build.lib.vfs.FileSystemUtils;
@@ -118,7 +118,7 @@
     Map<PackageIdentifier, Set<Root>> dirRootsMap = Maps.newTreeMap();
     for (Map.Entry<PackageIdentifier, Root> entry : packageRoots.entrySet()) {
       PackageIdentifier pkgId = entry.getKey();
-      if (pkgId.equals(Label.EXTERNAL_PACKAGE_IDENTIFIER)) {
+      if (pkgId.equals(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER)) {
         // This isn't a "real" package, don't add it to the symlink tree.
         continue;
       }
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
index ecde524..bd8aab6 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/Label.java
@@ -58,9 +58,6 @@
 @ThreadSafe
 public final class Label
     implements Comparable<Label>, Serializable, SkylarkValue, SkyKey, CommandLineItem {
-  public static final PathFragment EXTERNAL_PACKAGE_NAME = PathFragment.create("external");
-  public static final PathFragment WORKSPACE_FILE_NAME = PathFragment.create("WORKSPACE");
-  public static final String DEFAULT_REPOSITORY_DIRECTORY = "__main__";
 
   /**
    * Package names that aren't made relative to the current repository because they mean special
@@ -75,12 +72,8 @@
           // Visibility is labels aren't actually targets
           PathFragment.create("visibility"),
           // There is only one //external package
-          Label.EXTERNAL_PACKAGE_NAME);
+          LabelConstants.EXTERNAL_PACKAGE_NAME);
 
-  public static final PackageIdentifier EXTERNAL_PACKAGE_IDENTIFIER =
-      PackageIdentifier.createInMainRepo(EXTERNAL_PACKAGE_NAME);
-
-  public static final PathFragment EXTERNAL_PATH_PREFIX = PathFragment.create("external");
   public static final SkyFunctionName TRANSITIVE_TRAVERSAL =
       SkyFunctionName.createHermetic("TRANSITIVE_TRAVERSAL");
 
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/LabelConstants.java b/src/main/java/com/google/devtools/build/lib/cmdline/LabelConstants.java
new file mode 100644
index 0000000..b6c3d72
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/LabelConstants.java
@@ -0,0 +1,26 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.build.lib.cmdline;
+
+import com.google.devtools.build.lib.vfs.PathFragment;
+
+/** Constants associated with {@code Label}s */
+public class LabelConstants {
+  public static final PathFragment EXTERNAL_PACKAGE_NAME = PathFragment.create("external");
+  public static final PackageIdentifier EXTERNAL_PACKAGE_IDENTIFIER =
+      PackageIdentifier.createInMainRepo(EXTERNAL_PACKAGE_NAME);
+  public static final PathFragment EXTERNAL_PATH_PREFIX = PathFragment.create("external");
+  public static final PathFragment WORKSPACE_FILE_NAME = PathFragment.create("WORKSPACE");
+  public static final String DEFAULT_REPOSITORY_DIRECTORY = "__main__";
+}
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
index 732e6a0..4db5bf6 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
@@ -86,7 +86,7 @@
         ? Preconditions.checkNotNull(
             execPath.getParentDirectory(), "Must pass in files, not root directory")
         : execPath;
-    if (tofind.startsWith(Label.EXTERNAL_PATH_PREFIX)) {
+    if (tofind.startsWith(LabelConstants.EXTERNAL_PATH_PREFIX)) {
       // TODO(ulfjack): Remove this when kchodorow@'s exec root rearrangement has been rolled out.
       RepositoryName repository = RepositoryName.create("@" + tofind.getSegment(1));
       return PackageIdentifier.create(repository, tofind.subFragment(2));
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
index 1678c81..b914a75 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/RepositoryName.java
@@ -140,7 +140,7 @@
    * was invalid.
    */
   public static Pair<RepositoryName, PathFragment> fromPathFragment(PathFragment path) {
-    if (path.segmentCount() < 2 || !path.startsWith(Label.EXTERNAL_PATH_PREFIX)) {
+    if (path.segmentCount() < 2 || !path.startsWith(LabelConstants.EXTERNAL_PATH_PREFIX)) {
       return null;
     }
     try {
@@ -223,7 +223,8 @@
    */
   public PathFragment getSourceRoot() {
     return isDefault() || isMain()
-        ? PathFragment.EMPTY_FRAGMENT : Label.EXTERNAL_PACKAGE_NAME.getRelative(strippedName());
+        ? PathFragment.EMPTY_FRAGMENT
+        : LabelConstants.EXTERNAL_PACKAGE_NAME.getRelative(strippedName());
   }
 
   /**
@@ -233,7 +234,7 @@
   public PathFragment getPathUnderExecRoot() {
     return isDefault() || isMain()
         ? PathFragment.EMPTY_FRAGMENT
-        : Label.EXTERNAL_PATH_PREFIX.getRelative(strippedName());
+        : LabelConstants.EXTERNAL_PATH_PREFIX.getRelative(strippedName());
   }
 
   /**
diff --git a/src/main/java/com/google/devtools/build/lib/packages/Package.java b/src/main/java/com/google/devtools/build/lib/packages/Package.java
index ac19cef..58c93fe 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Package.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Package.java
@@ -23,6 +23,7 @@
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
@@ -246,7 +247,7 @@
    */
   public ImmutableMap<RepositoryName, RepositoryName> getRepositoryMapping(
       RepositoryName repository) {
-    if (!packageIdentifier.equals(Label.EXTERNAL_PACKAGE_IDENTIFIER)) {
+    if (!packageIdentifier.equals(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER)) {
       throw new UnsupportedOperationException("Can only access the external package repository"
           + "mappings from the //external package");
     }
@@ -266,7 +267,7 @@
    */
   public ImmutableMap<RepositoryName, ImmutableMap<RepositoryName, RepositoryName>>
       getExternalPackageRepositoryMappings() {
-    if (!packageIdentifier.equals(Label.EXTERNAL_PACKAGE_IDENTIFIER)) {
+    if (!packageIdentifier.equals(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER)) {
       throw new UnsupportedOperationException(
           "Can only access the external package repository"
               + "mappings from the //external package");
@@ -740,8 +741,9 @@
 
   public static Builder newExternalPackageBuilder(
       Builder.Helper helper, RootedPath workspacePath, String runfilesPrefix) {
-    Builder b = new Builder(helper.createFreshPackage(
-        Label.EXTERNAL_PACKAGE_IDENTIFIER, runfilesPrefix));
+    Builder b =
+        new Builder(
+            helper.createFreshPackage(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER, runfilesPrefix));
     b.setFilename(workspacePath);
     return b;
   }
@@ -876,7 +878,7 @@
 
     /** Determine if we are in the WORKSPACE file or not */
     boolean isWorkspace() {
-      return pkg.getPackageIdentifier().equals(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+      return pkg.getPackageIdentifier().equals(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
     }
 
     String getPackageWorkspaceName() {
diff --git a/src/main/java/com/google/devtools/build/lib/packages/PackageFactory.java b/src/main/java/com/google/devtools/build/lib/packages/PackageFactory.java
index 189876b..b482d92 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/PackageFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/PackageFactory.java
@@ -24,6 +24,7 @@
 import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import com.google.devtools.build.lib.analysis.skylark.BazelStarlarkContext;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.LabelValidator;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
@@ -1334,7 +1335,9 @@
         newExternalPackageBuilder(
                 RootedPath.toRootedPath(
                     buildFile.getRoot(),
-                    buildFile.getRootRelativePath().getRelative(Label.WORKSPACE_FILE_NAME)),
+                    buildFile
+                        .getRootRelativePath()
+                        .getRelative(LabelConstants.WORKSPACE_FILE_NAME)),
                 "TESTING")
             .build();
     return createPackageForTesting(
diff --git a/src/main/java/com/google/devtools/build/lib/packages/WorkspaceFactory.java b/src/main/java/com/google/devtools/build/lib/packages/WorkspaceFactory.java
index 24cfdfe..65b3093 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/WorkspaceFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/WorkspaceFactory.java
@@ -21,6 +21,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.LabelValidator;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
@@ -156,7 +157,7 @@
     BuildFileAST buildFileAST = BuildFileAST.parseBuildFile(source, localReporter);
     if (buildFileAST.containsErrors()) {
       throw new BuildFileContainsErrorsException(
-          Label.EXTERNAL_PACKAGE_IDENTIFIER, "Failed to parse " + source.getPath());
+          LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER, "Failed to parse " + source.getPath());
     }
     execute(buildFileAST, null, skylarkSemantics, localReporter);
   }
diff --git a/src/main/java/com/google/devtools/build/lib/pkgcache/PathPackageLocator.java b/src/main/java/com/google/devtools/build/lib/pkgcache/PathPackageLocator.java
index b0c780b..71c8f84 100644
--- a/src/main/java/com/google/devtools/build/lib/pkgcache/PathPackageLocator.java
+++ b/src/main/java/com/google/devtools/build/lib/pkgcache/PathPackageLocator.java
@@ -17,7 +17,7 @@
 import com.google.common.base.Preconditions;
 import com.google.common.base.Verify;
 import com.google.common.collect.ImmutableList;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.events.EventHandler;
@@ -249,7 +249,7 @@
     AtomicReference<? extends UnixGlob.FilesystemCalls> cache = UnixGlob.DEFAULT_SYSCALLS_REF;
     // TODO(bazel-team): correctness in the presence of changes to the location of the WORKSPACE
     // file.
-    return getFilePath(Label.WORKSPACE_FILE_NAME, cache);
+    return getFilePath(LabelConstants.WORKSPACE_FILE_NAME, cache);
   }
 
   private Path getFilePath(PathFragment suffix,
diff --git a/src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java b/src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java
index 17db2618f..9adfae7 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java
@@ -14,7 +14,7 @@
 package com.google.devtools.build.lib.query2;
 
 import com.google.common.collect.Iterables;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.collect.compacthashset.CompactHashSet;
 import com.google.devtools.build.lib.packages.Target;
 import com.google.devtools.build.lib.query2.engine.Callback;
@@ -36,7 +36,7 @@
   // deal with at once. A value of 100 was chosen experimentally.
   private static final int PROCESS_RESULTS_BATCH_SIZE = 100;
   private static final SkyKey EXTERNAL_PACKAGE_KEY =
-      PackageValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+      PackageValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
   private final SkyQueryEnvironment env;
   private final QueryExpressionContext<Target> context;
 
diff --git a/src/main/java/com/google/devtools/build/lib/query2/SkyQueryEnvironment.java b/src/main/java/com/google/devtools/build/lib/query2/SkyQueryEnvironment.java
index 5e81ec8..47c9786 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/SkyQueryEnvironment.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/SkyQueryEnvironment.java
@@ -42,6 +42,7 @@
 import com.google.common.util.concurrent.ThreadFactoryBuilder;
 import com.google.devtools.build.lib.actions.FileStateValue;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.cmdline.TargetParsingException;
 import com.google.devtools.build.lib.cmdline.TargetPattern;
@@ -1014,13 +1015,15 @@
   private static Iterable<SkyKey> getPkgLookupKeysForFile(PathFragment originalFileFragment,
       PathFragment currentPathFragment) {
     if (originalFileFragment.equals(currentPathFragment)
-        && originalFileFragment.equals(Label.WORKSPACE_FILE_NAME)) {
+        && originalFileFragment.equals(LabelConstants.WORKSPACE_FILE_NAME)) {
       // TODO(mschaller): this should not be checked at runtime. These are constants!
       Preconditions.checkState(
-          Label.WORKSPACE_FILE_NAME.getParentDirectory().equals(PathFragment.EMPTY_FRAGMENT),
-          Label.WORKSPACE_FILE_NAME);
+          LabelConstants.WORKSPACE_FILE_NAME
+              .getParentDirectory()
+              .equals(PathFragment.EMPTY_FRAGMENT),
+          LabelConstants.WORKSPACE_FILE_NAME);
       return ImmutableList.of(
-          PackageLookupValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER),
+          PackageLookupValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER),
           PackageLookupValue.key(PackageIdentifier.createInMainRepo(PathFragment.EMPTY_FRAGMENT)));
     }
     PathFragment parentPathFragment = currentPathFragment.getParentDirectory();
diff --git a/src/main/java/com/google/devtools/build/lib/repository/ExternalPackageUtil.java b/src/main/java/com/google/devtools/build/lib/repository/ExternalPackageUtil.java
index aa67974..b787d73 100644
--- a/src/main/java/com/google/devtools/build/lib/repository/ExternalPackageUtil.java
+++ b/src/main/java/com/google/devtools/build/lib/repository/ExternalPackageUtil.java
@@ -19,7 +19,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Lists;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.events.Event;
 import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
 import com.google.devtools.build.lib.packages.Package;
@@ -47,12 +47,13 @@
   private static List<Rule> getRules(
       Environment env, boolean returnFirst, Function<Package, List<Rule>> selector)
       throws ExternalPackageException, InterruptedException {
-    SkyKey packageLookupKey = PackageLookupValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+    SkyKey packageLookupKey = PackageLookupValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
     PackageLookupValue packageLookupValue = (PackageLookupValue) env.getValue(packageLookupKey);
     if (packageLookupValue == null) {
       return null;
     }
-    RootedPath workspacePath = packageLookupValue.getRootedPath(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+    RootedPath workspacePath =
+        packageLookupValue.getRootedPath(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
 
     List<Rule> rules = returnFirst ? ImmutableList.of() : Lists.newArrayList();
     SkyKey workspaceKey = WorkspaceFileValue.key(workspacePath);
@@ -66,7 +67,7 @@
         Event.replayEventsOn(env.getListener(), externalPackage.getEvents());
         throw new ExternalPackageException(
             new BuildFileContainsErrorsException(
-                Label.EXTERNAL_PACKAGE_IDENTIFIER, "Could not load //external package"),
+                LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER, "Could not load //external package"),
             Transience.PERSISTENT);
       }
       List<Rule> results = selector.apply(externalPackage);
diff --git a/src/main/java/com/google/devtools/build/lib/repository/ExternalRuleNotFoundException.java b/src/main/java/com/google/devtools/build/lib/repository/ExternalRuleNotFoundException.java
index 7534bcb..158890e 100644
--- a/src/main/java/com/google/devtools/build/lib/repository/ExternalRuleNotFoundException.java
+++ b/src/main/java/com/google/devtools/build/lib/repository/ExternalRuleNotFoundException.java
@@ -14,7 +14,7 @@
 
 package com.google.devtools.build.lib.repository;
 
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
 
 /** Exception thrown when a rule cannot be found. */
@@ -22,7 +22,7 @@
   public ExternalRuleNotFoundException(String ruleName) {
     super(
         new BuildFileContainsErrorsException(
-            Label.EXTERNAL_PACKAGE_IDENTIFIER,
+            LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
             "The rule named '" + ruleName + "' could not be resolved"),
         Transience.PERSISTENT);
   }
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
index 27a7c17..40ff497 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
@@ -46,7 +46,7 @@
 import com.google.devtools.build.lib.actions.extra.CppCompileInfo;
 import com.google.devtools.build.lib.actions.extra.EnvironmentVariable;
 import com.google.devtools.build.lib.actions.extra.ExtraActionInfo;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.collect.CollectionUtils;
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
 import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
@@ -866,8 +866,8 @@
         continue;
       }
       // One starting ../ is okay for getting to a sibling repository.
-      if (includePath.startsWith(Label.EXTERNAL_PATH_PREFIX)) {
-        includePath = includePath.relativeTo(Label.EXTERNAL_PATH_PREFIX);
+      if (includePath.startsWith(LabelConstants.EXTERNAL_PATH_PREFIX)) {
+        includePath = includePath.relativeTo(LabelConstants.EXTERNAL_PATH_PREFIX);
       }
       if (includePath.isAbsolute() || includePath.containsUplevelReferences()) {
         throw new ActionExecutionException(
diff --git a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
index bf3a52a..b03bfc2 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/repository/RepositoryFunction.java
@@ -24,6 +24,7 @@
 import com.google.devtools.build.lib.analysis.BlazeDirectories;
 import com.google.devtools.build.lib.analysis.RuleDefinition;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.LabelValidator;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
@@ -121,7 +122,7 @@
     public RepositoryNotFoundException(String repositoryName) {
       super(
           new BuildFileContainsErrorsException(
-              Label.EXTERNAL_PACKAGE_IDENTIFIER,
+              LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
               "The repository named '" + repositoryName + "' could not be resolved"),
           Transience.PERSISTENT);
     }
@@ -491,7 +492,7 @@
   }
 
   protected static Path getExternalRepositoryDirectory(BlazeDirectories directories) {
-    return directories.getOutputBase().getRelative(Label.EXTERNAL_PACKAGE_NAME);
+    return directories.getOutputBase().getRelative(LabelConstants.EXTERNAL_PACKAGE_NAME);
   }
 
   /**
diff --git a/src/main/java/com/google/devtools/build/lib/rules/repository/ResolvedFileFunction.java b/src/main/java/com/google/devtools/build/lib/rules/repository/ResolvedFileFunction.java
index 5766cdc..3bb1d18 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/repository/ResolvedFileFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/repository/ResolvedFileFunction.java
@@ -17,14 +17,13 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.actions.FileValue;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.packages.BazelLibrary;
 import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
 import com.google.devtools.build.lib.packages.NoSuchThingException;
 import com.google.devtools.build.lib.rules.repository.ResolvedFileValue.ResolvedFileKey;
 import com.google.devtools.build.lib.skyframe.PrecomputedValue;
 import com.google.devtools.build.lib.syntax.BuildFileAST;
-import com.google.devtools.build.lib.syntax.Environment;
 import com.google.devtools.build.lib.syntax.Mutability;
 import com.google.devtools.build.lib.syntax.ParserInputSource;
 import com.google.devtools.build.lib.syntax.SkylarkSemantics;
@@ -70,7 +69,7 @@
         if (ast.containsErrors()) {
           throw new ResolvedFileFunctionException(
               new BuildFileContainsErrorsException(
-                  Label.EXTERNAL_PACKAGE_IDENTIFIER,
+                  LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
                   "Failed to parse file resolved file " + key.getPath()));
         }
         com.google.devtools.build.lib.syntax.Environment resolvedEnvironment;
@@ -83,7 +82,7 @@
           if (!ast.exec(resolvedEnvironment, env.getListener())) {
             throw new ResolvedFileFunctionException(
                 new BuildFileContainsErrorsException(
-                    Label.EXTERNAL_PACKAGE_IDENTIFIER,
+                    LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
                     "Failed to evaluate resolved file " + key.getPath()));
           }
         }
@@ -91,24 +90,25 @@
         if (resolved == null) {
           throw new ResolvedFileFunctionException(
               new BuildFileContainsErrorsException(
-                  Label.EXTERNAL_PACKAGE_IDENTIFIER,
+                  LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
                   "Symbol 'resolved' not exported in resolved file " + key.getPath()));
         }
         if (!(resolved instanceof List)) {
           throw new ResolvedFileFunctionException(
               new BuildFileContainsErrorsException(
-                  Label.EXTERNAL_PACKAGE_IDENTIFIER,
-                      "Symbol 'resolved' in resolved file " + key.getPath() + " not a list"));
+                  LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
+                  "Symbol 'resolved' in resolved file " + key.getPath() + " not a list"));
         }
         ImmutableList.Builder<Map<String, Object>> result
             = new ImmutableList.Builder<Map<String, Object>>();
         for (Object entry : (List) resolved) {
           if (!(entry instanceof Map)) {
-          throw new ResolvedFileFunctionException(
-              new BuildFileContainsErrorsException(
-                  Label.EXTERNAL_PACKAGE_IDENTIFIER,
-                      "Symbol 'resolved' in resolved file " + key.getPath()
-                      + " contains a non-map entry"));
+            throw new ResolvedFileFunctionException(
+                new BuildFileContainsErrorsException(
+                    LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
+                    "Symbol 'resolved' in resolved file "
+                        + key.getPath()
+                        + " contains a non-map entry"));
           }
           ImmutableMap.Builder<String, Object> entryBuilder
               = new ImmutableMap.Builder<String, Object>();
@@ -117,8 +117,9 @@
             if (!(attribute instanceof String)) {
               throw new ResolvedFileFunctionException(
                   new BuildFileContainsErrorsException(
-                      Label.EXTERNAL_PACKAGE_IDENTIFIER,
-                          "Symbol 'resolved' in resolved file " + key.getPath()
+                      LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
+                      "Symbol 'resolved' in resolved file "
+                          + key.getPath()
                           + " contains a non-string key in one of its entries"));
             }
             entryBuilder.put((String) attribute, keyValue.getValue());
diff --git a/src/main/java/com/google/devtools/build/lib/rules/repository/WorkspaceAttributeMapper.java b/src/main/java/com/google/devtools/build/lib/rules/repository/WorkspaceAttributeMapper.java
index 0328462..812c708 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/repository/WorkspaceAttributeMapper.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/repository/WorkspaceAttributeMapper.java
@@ -17,7 +17,7 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.common.base.Preconditions;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.packages.AggregatingAttributeMapper;
 import com.google.devtools.build.lib.packages.BuildType.SelectorList;
 import com.google.devtools.build.lib.packages.Rule;
@@ -64,8 +64,10 @@
     Object value = rule.getAttributeContainer().getAttr(checkNotNull(attributeName));
     if (value instanceof SelectorList) {
       String message;
-      if (rule.getLocation().getPath().getBaseName().equals(
-          Label.WORKSPACE_FILE_NAME.getPathString())) {
+      if (rule.getLocation()
+          .getPath()
+          .getBaseName()
+          .equals(LabelConstants.WORKSPACE_FILE_NAME.getPathString())) {
         message = "select() cannot be used in WORKSPACE files";
       } else {
         message = "select() cannot be used in macros called from WORKSPACE files";
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ExternalFilesHelper.java b/src/main/java/com/google/devtools/build/lib/skyframe/ExternalFilesHelper.java
index 3331fda..aa7f036 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ExternalFilesHelper.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ExternalFilesHelper.java
@@ -15,7 +15,7 @@
 
 import com.google.common.base.Preconditions;
 import com.google.devtools.build.lib.analysis.BlazeDirectories;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadCompatible;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
 import com.google.devtools.build.lib.pkgcache.PathPackageLocator;
@@ -183,7 +183,7 @@
       return FileType.EXTERNAL;
     }
     if (rootedPath.asPath().startsWith(outputBase)) {
-      Path externalRepoDir = outputBase.getRelative(Label.EXTERNAL_PACKAGE_NAME);
+      Path externalRepoDir = outputBase.getRelative(LabelConstants.EXTERNAL_PACKAGE_NAME);
       if (rootedPath.asPath().startsWith(externalRepoDir)) {
         anyNonOutputExternalFilesSeen = true;
         return FileType.EXTERNAL_REPO;
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/LocalRepositoryLookupFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/LocalRepositoryLookupFunction.java
index cb1012d..7dbe529 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/LocalRepositoryLookupFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/LocalRepositoryLookupFunction.java
@@ -18,7 +18,7 @@
 import com.google.common.collect.Iterables;
 import com.google.devtools.build.lib.actions.FileValue;
 import com.google.devtools.build.lib.actions.InconsistentFilesystemException;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
 import com.google.devtools.build.lib.events.Event;
@@ -146,7 +146,7 @@
       externalPackageLookupValue =
           (PackageLookupValue)
               env.getValueOrThrow(
-                  PackageLookupValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER),
+                  PackageLookupValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER),
                   BuildFileNotFoundException.class,
                   InconsistentFilesystemException.class);
       if (externalPackageLookupValue == null) {
@@ -165,7 +165,7 @@
     }
 
     RootedPath workspacePath =
-        externalPackageLookupValue.getRootedPath(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+        externalPackageLookupValue.getRootedPath(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
 
     SkyKey workspaceKey = WorkspaceFileValue.key(workspacePath);
     do {
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
index d580796..3f03429 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/PackageFunction.java
@@ -29,6 +29,7 @@
 import com.google.devtools.build.lib.actions.InconsistentFilesystemException;
 import com.google.devtools.build.lib.clock.BlazeClock;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
@@ -291,8 +292,8 @@
     if (skylarkSemantics == null) {
       return null;
     }
-    RootedPath workspacePath = RootedPath.toRootedPath(
-        packageLookupPath, Label.WORKSPACE_FILE_NAME);
+    RootedPath workspacePath =
+        RootedPath.toRootedPath(packageLookupPath, LabelConstants.WORKSPACE_FILE_NAME);
     SkyKey workspaceKey = ExternalPackageFunction.key(workspacePath);
     PackageValue workspace = null;
     try {
@@ -308,7 +309,7 @@
     } catch (IOException | EvalException | SkylarkImportFailedException e) {
       throw new PackageFunctionException(
           new NoSuchPackageException(
-              Label.EXTERNAL_PACKAGE_IDENTIFIER,
+              LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
               "Error encountered while dealing with the WORKSPACE file: " + e.getMessage()),
           Transience.PERSISTENT);
     }
@@ -370,7 +371,7 @@
       }
     }
 
-    if (packageId.equals(Label.EXTERNAL_PACKAGE_IDENTIFIER)) {
+    if (packageId.equals(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER)) {
       return getExternalPackage(env, packageLookupValue.getRoot());
     }
     WorkspaceNameValue workspaceNameValue =
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/PackageLookupFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/PackageLookupFunction.java
index b3496b0..32e1b69 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/PackageLookupFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/PackageLookupFunction.java
@@ -18,7 +18,7 @@
 import com.google.common.collect.ImmutableSet;
 import com.google.devtools.build.lib.actions.FileValue;
 import com.google.devtools.build.lib.actions.InconsistentFilesystemException;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelValidator;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.packages.BuildFileName;
@@ -79,7 +79,7 @@
 
     if (!packageKey.getRepository().isMain()) {
       return computeExternalPackageLookupValue(skyKey, env, packageKey);
-    } else if (packageKey.equals(Label.EXTERNAL_PACKAGE_IDENTIFIER)) {
+    } else if (packageKey.equals(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER)) {
       return computeWorkspacePackageLookupValue(env, pkgLocator.getPathEntries());
     }
 
@@ -272,7 +272,10 @@
       throws PackageLookupFunctionException, InterruptedException {
     PackageLookupValue result =
         getPackageLookupValue(
-            env, packagePathEntries, Label.EXTERNAL_PACKAGE_IDENTIFIER, BuildFileName.WORKSPACE);
+            env,
+            packagePathEntries,
+            LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
+            BuildFileName.WORKSPACE);
     if (result == null) {
       return null;
     }
@@ -286,10 +289,11 @@
       return PackageLookupValue.NO_BUILD_FILE_VALUE;
     }
     Root lastPackagePath = packagePathEntries.get(packagePathEntries.size() - 1);
-    FileValue lastPackagePackagePathFileValue = getFileValue(
-        RootedPath.toRootedPath(lastPackagePath, PathFragment.EMPTY_FRAGMENT),
-        env,
-        Label.EXTERNAL_PACKAGE_IDENTIFIER);
+    FileValue lastPackagePackagePathFileValue =
+        getFileValue(
+            RootedPath.toRootedPath(lastPackagePath, PathFragment.EMPTY_FRAGMENT),
+            env,
+            LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
     if (lastPackagePackagePathFileValue == null) {
       return null;
     }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ProcessPackageDirectory.java b/src/main/java/com/google/devtools/build/lib/skyframe/ProcessPackageDirectory.java
index 71155a7..5ff75e8 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ProcessPackageDirectory.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ProcessPackageDirectory.java
@@ -21,7 +21,7 @@
 import com.google.devtools.build.lib.actions.FileValue;
 import com.google.devtools.build.lib.actions.InconsistentFilesystemException;
 import com.google.devtools.build.lib.analysis.BlazeDirectories;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
 import com.google.devtools.build.lib.events.Event;
@@ -188,7 +188,7 @@
       }
       String basename = dirent.getName();
       PathFragment subdirectory = rootRelativePath.getRelative(basename);
-      if (subdirectory.equals(Label.EXTERNAL_PACKAGE_NAME)) {
+      if (subdirectory.equals(LabelConstants.EXTERNAL_PACKAGE_NAME)) {
         // Not a real package.
         continue;
       }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunction.java
index ed5b15d..e5b3012 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredExecutionPlatformsFunction.java
@@ -25,6 +25,7 @@
 import com.google.devtools.build.lib.analysis.platform.PlatformInfo;
 import com.google.devtools.build.lib.analysis.platform.PlatformProviderUtils;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.TargetParsingException;
 import com.google.devtools.build.lib.packages.Package;
 import com.google.devtools.build.lib.packages.RuleClass;
@@ -109,7 +110,7 @@
   public static List<String> getWorkspaceExecutionPlatforms(Environment env)
       throws InterruptedException {
     PackageValue externalPackageValue =
-        (PackageValue) env.getValue(PackageValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER));
+        (PackageValue) env.getValue(PackageValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER));
     if (externalPackageValue == null) {
       return null;
     }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunction.java
index 1bb553e..c839e4c 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunction.java
@@ -23,6 +23,7 @@
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
 import com.google.devtools.build.lib.analysis.platform.DeclaredToolchainInfo;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.TargetParsingException;
 import com.google.devtools.build.lib.packages.Package;
 import com.google.devtools.build.lib.pkgcache.FilteringPolicies;
@@ -111,7 +112,7 @@
   @VisibleForTesting
   public static List<String> getRegisteredToolchains(Environment env) throws InterruptedException {
     PackageValue externalPackageValue =
-        (PackageValue) env.getValue(PackageValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER));
+        (PackageValue) env.getValue(PackageValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER));
     if (externalPackageValue == null) {
       return null;
     }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/RepositoryMappingFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/RepositoryMappingFunction.java
index 51e697a..0dcf235 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/RepositoryMappingFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/RepositoryMappingFunction.java
@@ -15,7 +15,7 @@
 package com.google.devtools.build.lib.skyframe;
 
 import com.google.common.collect.ImmutableMap;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.RepositoryName;
 import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
 import com.google.devtools.build.lib.packages.Package;
@@ -32,7 +32,7 @@
   @Override
   public SkyValue compute(SkyKey skyKey, Environment env)
       throws SkyFunctionException, InterruptedException {
-    SkyKey externalPackageKey = PackageValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+    SkyKey externalPackageKey = PackageValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
     PackageValue externalPackageValue = (PackageValue) env.getValue(externalPackageKey);
     if (env.valuesMissing()) {
       return null;
@@ -56,7 +56,7 @@
   private class RepositoryMappingFunctionException extends SkyFunctionException {
     RepositoryMappingFunctionException() {
       super(
-          new BuildFileContainsErrorsException(Label.EXTERNAL_PACKAGE_IDENTIFIER),
+          new BuildFileContainsErrorsException(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER),
           Transience.PERSISTENT);
     }
   }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/TargetPatternPhaseFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/TargetPatternPhaseFunction.java
index afd09b5..fa3db31 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/TargetPatternPhaseFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/TargetPatternPhaseFunction.java
@@ -23,6 +23,7 @@
 import com.google.common.collect.Iterables;
 import com.google.common.collect.Sets;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.ResolvedTargets;
 import com.google.devtools.build.lib.cmdline.TargetParsingException;
 import com.google.devtools.build.lib.events.Event;
@@ -72,8 +73,11 @@
     PackageValue packageValue = null;
     boolean workspaceError = false;
     try {
-      packageValue = (PackageValue) env.getValueOrThrow(
-          PackageValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER), NoSuchPackageException.class);
+      packageValue =
+          (PackageValue)
+              env.getValueOrThrow(
+                  PackageValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER),
+                  NoSuchPackageException.class);
     } catch (NoSuchPackageException e) {
       env.getListener().handle(Event.error(e.getMessage()));
       workspaceError = true;
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceASTFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceASTFunction.java
index 2d6942a..4e61794 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceASTFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceASTFunction.java
@@ -23,7 +23,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.actions.FileValue;
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
 import com.google.devtools.build.lib.packages.RuleClassProvider;
 import com.google.devtools.build.lib.rules.repository.RepositoryDelegatorFunction;
@@ -91,7 +91,8 @@
       if (ast.containsErrors()) {
         throw new WorkspaceASTFunctionException(
             new BuildFileContainsErrorsException(
-                Label.EXTERNAL_PACKAGE_IDENTIFIER, "Failed to parse default WORKSPACE file"),
+                LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
+                "Failed to parse default WORKSPACE file"),
             Transience.PERSISTENT);
       }
       if (newWorkspaceFileContents != null) {
@@ -114,7 +115,7 @@
         if (ast.containsErrors()) {
           throw new WorkspaceASTFunctionException(
               new BuildFileContainsErrorsException(
-                  Label.EXTERNAL_PACKAGE_IDENTIFIER, "Failed to parse WORKSPACE file"),
+                  LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER, "Failed to parse WORKSPACE file"),
               Transience.PERSISTENT);
         }
       }
@@ -129,7 +130,8 @@
       if (ast.containsErrors()) {
         throw new WorkspaceASTFunctionException(
             new BuildFileContainsErrorsException(
-                Label.EXTERNAL_PACKAGE_IDENTIFIER, "Failed to parse default WORKSPACE file suffix"),
+                LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER,
+                "Failed to parse default WORKSPACE file suffix"),
             Transience.PERSISTENT);
       }
       return new WorkspaceASTValue(splitAST(ast));
@@ -140,7 +142,7 @@
 
   private static WorkspaceASTFunctionException resolvedValueError(String message) {
     return new WorkspaceASTFunctionException(
-        new BuildFileContainsErrorsException(Label.EXTERNAL_PACKAGE_IDENTIFIER, message),
+        new BuildFileContainsErrorsException(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER, message),
         Transience.PERSISTENT);
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceNameFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceNameFunction.java
index 9284f5c..17f7c9a 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceNameFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/WorkspaceNameFunction.java
@@ -13,7 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.skyframe;
 
-import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.packages.BuildFileContainsErrorsException;
 import com.google.devtools.build.lib.packages.NoSuchPackageException;
 import com.google.devtools.build.lib.packages.Package;
@@ -34,7 +34,7 @@
   @Nullable
   public SkyValue compute(SkyKey skyKey, Environment env)
       throws InterruptedException, WorkspaceNameFunctionException {
-    SkyKey externalPackageKey = PackageValue.key(Label.EXTERNAL_PACKAGE_IDENTIFIER);
+    SkyKey externalPackageKey = PackageValue.key(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER);
     PackageValue externalPackageValue = (PackageValue) env.getValue(externalPackageKey);
     if (externalPackageValue == null) {
       return null;
@@ -54,7 +54,8 @@
 
   private class WorkspaceNameFunctionException extends SkyFunctionException {
     WorkspaceNameFunctionException() {
-      super(new BuildFileContainsErrorsException(Label.EXTERNAL_PACKAGE_IDENTIFIER),
+      super(
+          new BuildFileContainsErrorsException(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER),
           Transience.PERSISTENT);
     }
   }
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkImports.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkImports.java
index 9857f0f..fda4e0c 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkImports.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkImports.java
@@ -16,6 +16,7 @@
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableMap;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.cmdline.LabelConstants;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
 import com.google.devtools.build.lib.cmdline.LabelValidator;
 import com.google.devtools.build.lib.cmdline.PackageIdentifier;
@@ -198,7 +199,7 @@
         throw new SkylarkImportSyntaxException(MUST_HAVE_BZL_EXT_MSG);
       }
       PackageIdentifier packageId = importLabel.getPackageIdentifier();
-      if (packageId.equals(Label.EXTERNAL_PACKAGE_IDENTIFIER)) {
+      if (packageId.equals(LabelConstants.EXTERNAL_PACKAGE_IDENTIFIER)) {
         throw new SkylarkImportSyntaxException(EXTERNAL_PKG_NOT_ALLOWED_MSG);
       }
       return new AbsoluteLabelImport(importString, importLabel);